To be clear: should acpi_osi="Linux" fix the hardware mute showing up in the
mixer (and OSD appearing etc.)?
With 2.6.23.9-85.fc8 (on Thinkpad X61s), both with and without acpi_os="Linux",
the hardware mute works, but doesn't show up in the mixer (as per comment #5).
Keyboard in /etc/X11/xorg.conf is "gb+inet" ("gb+inet(thinkpad)", which some
sources suggest I might want, stops the volume buttons working).

my keyboard is "us+inet"
harware mute works both with and without acpi_osi="Linux"
adding acpi_osi="Linux" makes mixer respond to the "mute" button.
also before adding acpi_osi="Linux" xev wasn't detecting anything when pressing
the mute key, after adding it xev detects the key press.

Changing to us+inet does nothing for me (apart from mess up my keymap ;) )
Nothing from xev.
Which BIOS version are you using? I'm on 1.08 (7NET27WW). It looks like X61 and
X61s use the same BIOS. If you're running a newer version I'll try updating.

Hello,
I'm reviewing this bug as part of the kernel bug triage project, an attempt to
isolate current bugs in the Fedora kernel.
http://fedoraproject.org/wiki/KernelBugTriage
It appears as though the BIOS update may resolve the issue - is that correct?
If the problem no longer exists then please close this bug or I'll do so in a
few weeks if there is no additional information lodged.

I am currently using the latest BIOS update:
Version: 2.06
Release Date: 2007/12/28
and the latest Fedora 8 kernel-2.6.23.15-137.fc8
and the bug is still present.
Adding acpi_osi="Linux" kernel boot option fixes the problem.